In the past years, interest in using recycled asphalt pavement (RAP) has been growing rapidly. This rise in interest is motivated by a number of reasons including a desire to reduce cost, preserve the environment, and conserve energy. With the increasing bitumen prices and dwindling supply of higher quality virgin aggregate, there is a compelling need to use larger amounts of less expensive RAP to replace the more expensive virgin bitumen and aggregates. Despite the need to use higher proportions of RAP, a recent survey, conducted on the use of recycled materials in asphalt pavements, revealed that the average percentage of RAP in the United States has only increased from 15% in 2009 to 20% in 2014 (Hansen, et al., “Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage: 2014,” (2015)). This percentage is expected to increase in the near future as researchers gain more understanding of the mechanism of rejuvenators and its interaction with aged asphalt binder.
Such reluctance to use more RAP in asphalt pavements stems from the fact that the aged RAP bitumen has undesirable high stiffness and low creep rate, which makes it susceptible to low temperature thermal cracking (Yu et al., “Rheological, Microscopic, and Chemical Characterization of the Rejuvenating Effect on Asphalt Binders,” Fuel 135:162-171 (2014)). Accordingly, using higher percentages of RAP produces very stiff mixes which are difficult to field compact, and can result in unexpected premature failure (Copeland, A., “Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice,” (2011)).
Several techniques are being implemented to allow for the use of RAP in asphalt mixes, including mixing with a softer virgin bitumen, using higher asphalt content mixtures, and using warm-mix technology to minimize the short-term aging effect and to lower asphalt absorption (Im et al., “Development of New Mix Design Method for Asphalt Mixtures Containing RAP and Rejuvenators,” Construction and Building Materials 115:727-734 (2016)). These techniques are suitable for lower RAP content mixtures; however, they fail to allow for the use of higher RAP content. For instance, the use of softer virgin bitumen would compensate the aging of the RAP bitumen for low RAP content mixes but its effect on high RAP content mixes would be insignificant (West et al., “Improved Mix Design, Evaluation, and Materials Management Practices for Hot Mix Asphalt with High Reclaimed Asphalt Pavement Content,” Transportation Research Board (2013)). In this regard, rejuvenators have shown to be a very attractive alternative in that they can lead to higher RAP content. Rejuvenators have proven to be very efficient in restoring the aged bitumens to their original state. With the increase in popularity of hot-in-place pavement recycling (HIR), rejuvenators are becoming even more important. In HIR, old pavements are heated and milled in place before being mixed with virgin aggregates, virgin bitumen, and a rejuvenator.
Rejuvenators have been successfully implemented to offset the high stiffness and low creep rate of aged RAP asphalt binder. Use of rejuvenators has resulted in considerable improvement to low-temperature mix properties of mixtures with high RAP content (Hajj et al., “Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2371:13-22 (2013); Shen et al., “Effects of Rejuvenating Agents on Superpave Mixtures Containing Reclaimed Asphalt Pavement,” Journal of Materials in Civil Engineering 19(5):376-384 (2007); and Zaumanis et al., “Influence of Six Rejuvenators on the Performance Properties of Reclaimed Asphalt Pavement (RAP) Binder and 100% Recycled Asphalt Mixtures,” Construction and Building Materials 71:538-550 (2014)).
Asphalt is composed of four distinct chemical fractions, namely asphaltenes, resins, aromatics, and saturates. Resins, aromatics, and saturates are collectively referred to as maltenes. The high molecular weight asphaltenes form a colloidal suspension in low molecular weight maltenes. The asphaltene content has a great influence on asphalt viscosity. In a recent study, increasing the asphaltene content by addition of propane deasphaltene tar (PDA) resulted in a noticeable increase in the penetration index, and a similar effect was also noted with aging (Firoozifar et al., “The Effect of Asphaltene on Thermal Properties of Bitumen,” Chemical Engineering Research and Design 89(10):2044-2048 (2011)). Apart from the asphaltene content, the resins also play an important role since they act as dispersing agents to the asphaltenes. The ratio of resins to asphaltenes is an important parameter that controls the degree of dispersion of asphaltenes and accordingly the asphalt viscosity (Telford, T., THE SHELL BITUMEN INDUSTRIAL HANDBOOK (1995)).
Rejuvenators are chemical or bio-derived additives which typically contain a high proportion of maltenes, which serves to replenish the maltene content in the aged bitumen that has been lost as a result of oxidation leading to increased stiffness (Copeland, A., “Reclaimed Asphalt Pavement in Asphalt Mixtures: State of the Practice,” (2011)). Binder aging is characterized by a change of the maltenes fraction into asphaltene through oxidation. The amount of asphaltene is related to the viscosity of asphalt. Firoozifar et al., “The Effect of Asphaltene on Thermal Properties of Bitumen,” Chemical Engineering Research and Design 89:2044-2048 (2011). The addition of maltenes helps rebalance the chemical composition of the aged bitumen, which contain a high percentage of asphaltenes (causing high stiffness and low creep rate). Rejuvenators recreate the balance between the asphaltene and maltene by providing more maltenes and/or by allowing better dispersion of the asphaltenes (Elseifi et al., “Laboratory Evaluation of Asphalt Mixtures Containing Sustainable Technologies,” Journal of the Association of Asphalt Paving Technologists 80 (2011). Rejuvenators are added during mixing and are believed to diffuse within the aged bitumen imparting softening characteristics. The rejuvenator initially coats the outside of the RAP aggregates before they gradually seep into the aged bitumen layer until they diffuse through the film thickness (Carpenter et al., “Modifier Influence in the Characterization of Hot-Mix Recycled Material,” Transportation Research Record 777 (1980)). Improvement in the low temperature properties and stiffness of rejuvenated aged binders have been verified by a number of studies (Elseifi et al., “Laboratory Evaluation of Asphalt Mixtures Containing Sustainable Technologies,” Journal of the Association of Asphalt Paving Technologists 80 (2011) and Zaumanis et al., “Evaluation of Different Recycling Agents for Restoring Aged Asphalt Binder and Performance of 100% recycled asphalt,” Materials and Structures 48:2475-2488 (2015)). Several rejuvenators derived from petroleum based aromatic extracts, distilled tall oil, and organic oils have been successfully implemented (Zaumanis et al., “Influence of Six Rejuvenators on the Performance Properties of Reclaimed Asphalt Pavement (RAP) Binder and 100% Recycled Asphalt Mixtures,” Construction and Building Materials 71:538-550 (2014)).
A number of studies have investigated the performance of rejuvenated bitumens and resulting asphalt mixtures. The main focus of these studies was to investigate the effect of rejuvenators on the stiffness of the aged bitumen and the low temperature cracking resistance of the produced asphalt mixtures (Elseifi et al., “Laboratory Evaluation of Asphalt Mixtures Containing Sustainable Technologies,” Journal of the Association of Asphalt Paving Technologists 80 (2011); Zaumanis et al., “Evaluation of Rejuvenator's Effectiveness with Conventional Mix Testing for 100% Reclaimed Asphalt Pavement Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2370:17-25 (2013); Hajj et al., “Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2371:13-22 (2013)). It has been concluded that rejuvenators successfully reduce the aged bitumen stiffness and notably improve the low temperature cracking resistance of the resulting mixture (Mogawer et al., “Evaluating the Effect of Rejuvenators on the Degree of Blending and Performance of High RAP, RAS, and RAP/RAS Mixtures,” Road Materials and Pavement Design 14 (sup2): 193-213 (2013); Tran et al., “Effect of Rejuvenator on Performance Properties of HMA Mixtures With High RAP and RAS Contents,” Auburn, Ala.: National Center for Asphalt Technology (2012)). The selection of the rejuvenator dosage was found to have a great influence on the effectiveness of the treatment (Shen et al., “Effects of Rejuvenator on Performance-Based Properties of Rejuvenated Asphalt Binder and Mixtures,” Construction and Building Materials 21(5):958-964 (2007)). It was suggested that blending charts could be used to obtain an optimum dosage that meets the requirements of the bitumen specifications. Determining the proper dose is crucial since a higher dosage may cause undesirable excessive softening of the bitumen, which my lead to performance problems such as rutting. The rejuvenated bitumen properties can be determined through extraction of the aged bitumen, blending with the rejuvenator, and subsequent testing. Such technique, however, assumes perfect blending between the rejuvenator and the aged bitumen, which does not necessarily reflect actual conditions. During actual mixing, the rejuvenator might not diffuse fully through the aged asphalt film thickness.
The performance of mixes which involve RAP is controlled to a large extent by the degree of blending between the RAP bitumen and the virgin bitumen in addition to the effective percentage of RAP bitumen which contribute towards the total asphalt content (Huang et al., “Laboratory Investigation of Mixing Hot-Mix Asphalt With Reclaimed Asphalt Pavement,” Transportation Research Record. Journal of the Transportation Research Board 1929:37-45 (2005)). Through the use of rejuvenators, the RAP bitumen becomes less stiff and can thus blend more easily with the virgin bitumen.
Aged RAP bitumens are characterized as having a high relative viscosity. The high viscosity can lead to poor mixing and compaction, hence the study of the rejuvenator's effect in reducing the viscosity is very important. Achieving low viscosity ensures that the bitumen has sufficient flow to properly blend with the virgin bitumen and to uniformly coat both virgin and RAP aggregates. It is equally important for the rejuvenator to be able to lower the RAP bitumen viscosity to acceptable levels without the need for high dosages. High dosages of rejuvenators could lead to potential rutting, stripping and mix instability problems (Zaumanis et al., “Evaluation of Rejuvenator's Effectiveness with Conventional Mix Testing for 100% Reclaimed Asphalt Pavement Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2370:17-25 (2013)). The study of the temperature-viscosity dependence of the rejuvenated aged bitumen is also important because high mixing temperatures could damage the bitumen so it is advantageous to have an effective rejuvenator which would promote low mixing temperatures at a low dosage. Through reducing the viscosity, the RAP binder becomes less stiff and can thus blend more easily with the virgin binder. The degree of blending between the RAP binder and the virgin binder determines to a large extent the performance of mixtures containing RAP, by increasing the effective percentage of RAP binder that contributes to the total asphalt content (Huang et al., “Laboratory Investigation of Mixing Hot-Mix Asphalt With Reclaimed Asphalt Pavement,” Transportation Research Record. Journal of the Transportation Research Board 1929:37-45 (2005)). Being able to reduce viscosity, rejuvenators can help achieve sufficient flow at lower mixing temperatures. The relationship between viscosity and temperature should be well understood. A good rejuvenator should be capable of lowering the viscosity to acceptable levels without the need for high dosages.
Rejuvenators vary greatly according to their chemical composition and origin. Numerous research efforts have been directed to assessing the performance of commercially available rejuvenators, as well as proposing new materials to act as rejuvenators. Materials derived from distilled tall oil, petroleum based aromatic extract, and organic oil have been successfully applied as rejuvenators (Zaumanis et al., “Influence of Six Rejuvenators on The Performance Properties of Reclaimed Asphalt Pavement (RAP) Binder and 100% Recycled Asphalt Mixtures,” Construction and Building Materials 71:538-550 (2014)). Organic oil bio-derived rejuvenators have been presented as a safe alternative to the carcinogenic aromatic oil rejuvenators (Hajj et al., “Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2371:13-2 (2013)). Organic oils have been successfully used by the Florida Department of Transportation (FDOT) for mixes that contain 40% RAP. Two trial sections were constructed on 1-95 using 0.75% of organic oil by weight of RAP in 2009. Other DOTs have reported using organic oil at varying RAP contents such as the Texas DOT with 35% RAP and 5% RAS, and the New York City DOT with 20% RAP (Hajj et al., “Influence of Hydrogreen Bioasphalt on Viscoelastic Properties of Reclaimed Asphalt Mixtures,” Transportation Research Record. Journal of the Transportation Research Board 2371:13-2 (2013)). A study conducted in Zaumanis et al., “Influence of Six Rejuvenators on the Performance Properties of Reclaimed Asphalt Pavement (RAP) Binder and 100% Recycled Asphalt Mixtures,” Construction and Building Materials 71:538-550 (2014) investigated the performance of six different rejuvenators including waste engine oil, distilled tall oil, waste vegetable oil, waste vegetable grease, organic oil, and aromatic extract. The study was performed on mixes using 100% RAP, with a 12% rejuvenator dosage by mass of RAP bitumen. It was shown that organic-based rejuvenators were more efficient in lowering the low temperature performance grade (PG) of the rejuvenated bitumen compared to petroleum-based rejuvenators. It was also shown that none of the rejuvenators significantly reduced the high temperature PG, which indicates that with the use of an appropriate rejuvenator dosage, rutting should not be a concern. All of the six rejuvenators seemed to work efficiently at this dosage except for waste engine oil which did not meet the low temperature grade and resulted in high mass loss, which indicates volatility and increased aging susceptibility.
The durability of rejuvenators is crucial to their proper usage. Softening agents containing volatile compounds can only provide a temporary reduction in stiffness to aid compaction. Upon volatilization of these compounds, the softening agents can no longer provide additional enhancement to the mixture. Rejuvenators need to have a prolonged effect on the asphalt mixture properties.
A number of studies have addressed the issue of durability of rejuvenated asphalt. In the work reported in Shen et al., “Effects of Rejuvenating Agents on Superpave Mixtures Containing Reclaimed Asphalt Pavement,” Journal of Materials in Civil Engineering 19(5):376-384 (2007)), mixtures containing 48% RAP and 12.5% rejuvenator, by mass of RAP bitumen, were evaluated for rutting in an asphalt pavement analyzer (APA) and for moisture sensitivity using indirect tensile strength (ITS) tests. It was shown that the performance of the rejuvenated mixes was better than the control RAP mixes prepared with a softer virgin bitumen. A recent study investigated the long-term aging behavior of rejuvenated bitumen prepared using five different rejuvenators (Ali et. al., “Long-Term Aging of Recycled Binders” (2015)). It was revealed that the long-term aging effect differed greatly among rejuvenators. Two of the rejuvenators, namely aromatic extract and a water-based emulsion from naphthenic crude, caused slowing down of the aging rate compared to virgin bitumens while the other three, namely petroleum neutral distillate, oil-based bio-rejuvenator and a polyol ester pine, accelerated aging. Study of long-term cracking and fatigue resistance of rejuvenated mixes was performed on full-depth asphalt pavement specimens (Ali et. al., “Long-Term Aging of Recycled Binders” (2015)). The long-term aging was simulated using an Accelerated Pavement Weathering System (APWS). APWS simulates real weather conditions including rain, sunshine, and temperature fluctuations. The Texas Overlay Test, as described in TEX-248-F (Designation, T., “TEX-248-F,” Overlay Test, Construction Division, Texas Department of Transportation (2009)), was performed to assess fatigue and cracking resistance for specimens subjected to 0, 1000, and 3000 hours of APWS aging. The results indicated that the rejuvenated mixes showed better fatigue and reflective cracking resistance compared to the virgin mixes. It was shown that rejuvenated asphalt mixtures had better performance in terms of fatigue and reflective cracking compared to virgin asphalt mixtures, even after 3000 hours of APWS aging (Ali et. al., “Long-Term Aging of Recycled Binders” (2015)). The chemistry of the interaction between the rejuvenator and the binder is also very important. A recent study showed that an aromatic extract rejuvenator worked effectively for a PG58-10 and not as effectively with a PG58-28 binder (Yu et al., “Rheological, Microscopic, and Chemical Characterization of the Rejuvenating Effect on Asphalt Binders,” Fuel 135:162-171 (2014)).
Cracking induced by fatigue is considered a primary mode of distress in asphalt pavements. The viscoelastic properties of the asphalt binder determine to a great extent the fatigue performance of asphalt mixes (Bahia et al., “Characterization of Modified Asphalt Binders in SUPERPAVE MIX DESIGN (2001)). The fatigue resistance of binders is currently characterized using the fatigue parameter, G**sin δ. This parameter is determined using a Dynamic Shear Rheometer (DSR) measurements at 1% strain rate, as per AASHTO T315, to ensure that the binder remains within the linear viscoelastic region. Such an approach has failed to capture the performance of binders under destructive loading which results in accumulated damage (Bahia et al., “Characterization of Modified Asphalt Binders in SUPERPAVE MIX DESIGN (2001)). The Time sweep (TS) test was introduced based on the work done on NCHRP Project 9-10 (Bahia et al., “Characterization of Modified Asphalt Binders in SUPERPAVE MIX DESIGN (2001) and Bonnetti et al., “Measuring and Defining Fatigue Behavior of Asphalt Binders,” Transportation Research Record. Journal of the Transportation Research Board 1810:33-43 (2002)). The TS test is conducted using a DSR on an RTFO+PAV (long term+short term) aged binder with an 8-mm-diameter geometry. In this test a repeated cyclic load is applied under constant strain rate until failure. Failure is typically marked by a 50% drop in G* (Kim et al., “Fatigue Characterization of Asphalt Concrete Using Viscoelasticity and Continuum Damage Theory (With Discussion),” Journal of the Association of Asphalt Paving Technologists 66 (1997)). The choice of the constant strain rate at which to run the test is determined to reflect the pavement structure and traffic conditions. A major drawback of the TS test is the uncertainty in testing time and the fact that it can take several hours to perform. Additionally, such elongated testing time may cause steric hardening of the binder, which could skew the results (Planche et al., “Evaluation of Fatigue Properties of Bituminous Binders,” Materials and Structures 37(5):356-359 (2004)). Recently, the Linear amplitude sweep test (LAS) was introduced as an efficient test to characterize fatigue in binders (Johnson et al., “Practical Application of Viscoelastic Continuum Damage Theory to Asphalt Binder Fatigue Characterization,” Asphalt Paving Technology-Proceedings 28:597 (2009)). Similar to the TS test, the LAS test uses an 8-mm-diameter and a 2-mm gap geometry, to apply a repeated cyclic load to the binder sample. In the LAS test, however, an increasing strain rate is applied to induce accumulated damage. In a recent study that investigated the use of six different recycling agents on the fatigue life of 100% RAP mixtures, LAS testing was used to evaluate the number of cycles to failure for all rejuvenated blends (Zaumanis et al., “Evaluation of Different Recycling Agents for Restoring Aged Asphalt Binder and Performance of 100% Recycled Asphalt,” Materials and Structures 48(8):2475-2488 (2015)). It was concluded that the bioderived recycling agents were superior to the petroleum based recycling agents. The bioderived recycling agents increased the number of cycles to failure in the RAP binder to a level comparable to that of the virgin binder. In another study, LAS testing was used to assess the fatigue performance of a RAP binder blended with both a soft and a stiff virgin binder at both 20% and 50% RAP binder content. It was shown that the fatigue life increased with higher amounts of RAP binder. It was also concluded that using a softer binder in lieu of a stiff binder led to better performance compared to increasing the stiff virgin binder content (Willis et al., “Effects of Changing Virgin Binder Grade and Content on RAP Mixture Properties,” NCAT Report (12-03) (2012)).
Using RAP can have a great impact on the low temperature cracking potential of asphalt mixtures. Hence, it is important to assess the low temperature properties of mixtures prepared with RAP. The disk-shaped compact tension (DCT) is one of the commonly used tests to assess low temperature cracking resistance (Wagoner et al., “Investigation of the Fracture Resistance of Hot-Mix Asphalt Concrete Using a Disk-Shaped Compact Tension Test,” Transportation Research Record. Journal of the Transportation Research Board 1929:183-192 (2005)). The DCT test gives the fracture energy, in J/m2, for a crack to propagate through a notched specimen under a displacement-controlled tensile loading. A comprehensive study that correlated fracture energy to field performance showed that a fracture energy between 350-400 J/m2 marks a sufficient resistance against thermal and reflective cracking (Buttlar et al., “Comprehensive Database of Asphalt Concrete Fracture Energy and Links to Field Performance,” 89th Annual Meeting of the Transportation Research Board, 502 Washington, D.C. (2010)). Minimal occurrence of transverse cracking was found in mixtures with fracture energies above 400 J/m2 (Buttlar et al., “Comprehensive Database of Asphalt Concrete Fracture Energy and Links to Field Performance,” 89th Annual Meeting of the Transportation Research Board, 502 Washington, D.C. (2010)). A recent investigation that looked into the effect of different percentages of recycled materials into asphalt mixtures was conducted at Iowa State University and the University of Illinois Urbana-Champaign (Williams et al., “Characterization of Hot Mix Asphalt Containing Post-Consumer Recycled Asphalt Shingles and Fractionated Reclaimed Asphalt Pavement,” Report to the Illinois State Toll Highway Authority (2011)). This study looked at low temperature performance of eight different mixtures, containing various percentages of RAP and recycled asphalt shingles (RAS), used in the construction of Illinois Tollway (1-90). DCT testing done at −12° C. revealed that the fracture energy decreased with the addition of recycled materials, with the specimens containing 50% recycled materials failing to meet the minimum threshold of 350 J/m2 (Williams et al., “Characterization of Hot Mix Asphalt Containing Post-Consumer Recycled Asphalt Shingles and Fractionated Reclaimed Asphalt Pavement,” Report to the Illinois State Toll Highway Authority (2011)). DCT testing was also used to assess the effect of aging on the low temperature fracture behavior of asphalt mixtures (Braham et al., “The Effect of Long-Term Laboratory Aging on Asphalt Concrete Fracture Energy,” Journal of the Association of Asphalt Paving Technologists 78 (2009)). It was concluded that fracture energy decreased consistently with longer hours of aging. With aging, an increase in the peak load was noted followed by a steep drop in the load resulting in an overall less area under the load-displacement curve hence less fracture energy.
The effectiveness of a rejuvenator is also related to the bitumen's chemical composition. A specific rejuvenator could work effectively for one bitumen but not another. Two bitumens from different crude sources, namely AAD (PG 58-28) and ABD (PG 58-10), were rejuvenated using aromatic extract rejuvenators (Yu et al., “Rheological, Microscopic, and Chemical Characterization of the Rejuvenating Effect on Asphalt Binders,” Fuel 135:162-171 (2014)). The effect of rejuvenation on the low temperature grade was more pronounced on the ABD bitumen compared to the AAD bitumen, which was attributed to a better chemical interaction between the rejuvenator and the bitumen.
The changes in the chemical composition of the bitumen as a result of aging and rejuvenation can be examined using SARA fractionation. SARA fractionation can be used to detect changes in the different chemical fractions of asphalt due to aging and rejuvenation. PAV aging of virgin bitumen, followed by SARA fractionation, revealed conversion of aromatics to asphaltenes with no significant change in resins or saturates (Yu et al., “Rheological, Microscopic, and Chemical Characterization of the Rejuvenating Effect on Asphalt Binders,” Fuel 135:162-171 (2014)). Addition of an aromatic extract rejuvenator caused an increase in the content of saturates and aromatics accompanied by a reduction in the asphaltenes proportion. The chemical composition of the rejuvenated bitumen did not exactly mirror that of the virgin bitumen but the overall effect of the rejuvenation process was to introduce chemical changes that helped restore the virgin bitumen properties.
The United States produces about one third of the world soybean output (Iowa Soybean Association, “An Allocation of Iowa-Grown Soybean and The Resulting Soybean Meal and Oil” (2016)). The State of Iowa is considered one of the big producers of soybean in the U.S., according to a recent report published by the Iowa Soybean Association (Iowa Soybean Association (2016)). This substantial production mainly is used in making soybean meal or soybean oil. Soybean meals are largely consumed by the livestock industry while most of the soybean oil is used in the production of biodiesel fuel. An estimated 20% of the soybean output is used to make biodiesel oil (Iowa Soybean Association (2016)). The process of biodiesel oil production involves transesterification of the soybean oil in the presence of a catalyst (Ma et al., “Biodiesel Production: A Review,” Bioresource Technology 70(1):1-15 (1999)). The abundancy of the soybean oil production in the United States inspires the need to look for alternative applications other than biodiesel production.
A number of previous studies have used soybean oil derived materials in asphalt. Soybean acidulated soapstock (SAS), which is considered a rich source of soybean fatty acids, was used as a fluxing agent at dosages from 1-3%. Seidel et al., “Rheological Characterization of Asphalt Binders Modified With Soybean Fatty Acids,” Construction and Building Materials 53:324-332 (2014). There was a consistent decrease in the critical high temperature with the SAS modification. An enhancement in the low temperature was also observed. Another recent study used soybean oil as a warm-mix asphalt (WMA) additive, with dosages from 1-3%. It was concluded that an average reduction in the mixing and compaction temperature of 2.7° C. to 3.4° C. was attained. Portugal et al., “Rheological Performance of Soybean in Asphalt Binder Modification,” Road Materials and Pavement Design pp. 1-15 (2017).
Other than soybean oil, vegetable oils have been previously suggested as recycling agents or rejuvenators. Two-point bending tests performed on RAP mixtures modified with a vegetable oil based recycled agent showed improved fatigue performance and lower complex modulus (Mangiafico et al., “Complex Modulus and Fatigue Performances of Bituminous Mixtures With Reclaimed Asphalt Pavement and a Recycling Agent of Vegetable Origin,” Road Materials and Pavement Design 1-16 (2016)). Waste vegetable oil has been used to modify 100% RAP mixtures resulting in a reduced temperature performance grade (Zaumanis et al., “Influence of Six Rejuvenators on the Performance Properties of Reclaimed Asphalt Pavement (RAP) Binder and 100% Recycled Asphalt Mixtures,” Construction and Building Materials, 71, 538-550 (2014). Other bio-derived rejuvenators including distilled tall oil and cotton seed oil were also used to rejuvenate asphalt binders (Chen et al., “High Temperature Properties of Rejuvenating Recovered Binder With Rejuvenator, Waste Cooking and Cotton Seed Oils,” Construction and Building Materials 59:10-16 (2014) and Zaumanis et al., “Evaluation of Different Recycling Agents for Restoring Aged Asphalt Binder and Performance of 100% Recycled Asphalt,” Materials and Structures 48(8):2475-2488 (2015)).
Thermogravimetric analysis (TGA) is used to determine mass loss as a function of temperature. TGA can either be done in an inert environment using nitrogen or in an oxidative environment using air. An inert environment does not allow for combustion to occur. TGA under nitrogen has been previously used to characterize asphalt binders with different asphaltene contents. Firoozifar et al., “The Effect of Asphaltene on Thermal Properties of Bitumen,” Chemical Engineering Research and Design 89:2044-2048 (2011). A relation between the asphaltene content and the decomposition temperatures of asphalt was noted. The thermal stability decreased with more asphaltene content resulting in a lower char yield. Firoozifar et al., “The Effect of Asphaltene on Thermal Properties of Bitumen,” Chemical Engineering Research and Design 89:2044-2048 (2011). In a recent study, TGA of binder blends containing re-refined vacuum tower bottoms (RVTB) was performed under nitrogen and air to assess changes in the thermal stability. Wielinski et al., “Analysis of Vacuum Tower Asphalt Extender and Effect on Bitumen and Asphalt Properties,” Road Materials and Pavement Design 16:90-110 (2015). The binders were heated under nitrogen until the mass loss reached a plateau at around 600° C. Air was then introduced and the temperature raised to 800° C. to burn off the remaining constituents. The remaining mass referred to as ash was less than 2%. No significant changes in the thermal stability were noted between the neat binder and the binder blended with 9% RVTB. TGA was also used to characterize binders modified with styrene-butadiene-styrene polymer and tall oil pitch. Ahmedzade et al., “Laboratory Investigation of the Properties of Asphalt Concrete Mixtures Modified with TOP-SBS,” Construction and Building Materials 21:626-633 (2007). It was concluded that the modified binders were thermally stable at the mixing and compaction temperatures of asphalt concrete pavements. Recently, TGA was coupled with mass spectrometry to study chemical changes in aged binders. de Sá et al., “Weathering Degradation Effect on Chemical Structure of Asphalt Binder,” International Journal of Pavement Research and Technology 8:23-28 (2015). The TGA analysis was performed under a flow of argon up to a temperature of 900° C. It was noted that char yield decreased from 17% to 6% with aging.
The present invention is directed to overcoming these and other deficiencies in the art.